Velocity modulation tubes



Feb. 21, 1961 A. LERBS VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 1 Feb. 21, 1961 A. LERBS 2,972,701

v VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 2 INVENTOR Alfred vLERBS Feb. 21, 1961 A. LERBS VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 3 INVENTOR Alfred LERBS BY AQEQ/ I Feb. 21, 1961 A. LERBS VELOCITY MODULATION TUBES l5 Sheets-Sheet 4 Original Filed May 5, 1955 INVENTOR Alfred LERBS BY r: 4

Feb. 21, 1961 A. LERBS 2,972,701

VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 5 /5 m E 20 //2 .5 E

\9 INV ENTO R Alfred LERBS Feb. 21, 1961 A. LERBS VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 7 Feb. 21, 1961 LERBS 2,972,701

VELOCITY MODULATION TUBES 15 Sheets-Sheet 8 INVENTOR Alfred LERBS HQ QWEW 15 Sheets-Sheet 9 A. LERBS VELOCITY MODULATION TUBES Original Filed May 5, 1955 M m F Feb. 21, 1961 FIG. 19

INVENTOR Alfred LERBS BY gm Feb. 21, 1961 A. LERBS 2,972,701

VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 1o INVENTOR Alfred L'ERBS Feb. 21, 1961 LERBs 2,972,701

VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 11 I ENTOR Alfred LERBS BY A 0R M/- v m 4 s W/ 7\\/ 1/4. .H ml

Feb. 21, 1961 LERBS 2,972,701

VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 12 INVENTOR Alfred L'RBS Feb. 21, 1961 A. LERBS VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 13 INVENTOR Alfred LERBS BY 7?! Feb. 21, 1961 A. LERBS VELOCITY MODULATION TUBES Original Filed May 5, 1955 INVENTOR Alfred LERBS BY R Feb. 21, 1961 5 LERBs 2,972,701

VELOCITY MODULATION TUBES Original Filed May 5, 1955 15 Sheets-Sheet 15 FIG. 22

INVENTOR Alfred LERBS 2,972,701 VELOCITY MODULATION TUBES Alfred Lerbs, Paris, France, assignortto Cpmpagnie Generalede Telegraphic Sans'Fil, a corporation of France Original application 4 5, p 1955, Ser. No. "506,317, now Patent No. 2,938,139 datedMay 24, 1960. Drvided and this application July 6, 1959, Sen No. 829,174" V- I Claims priority, application France May 10, 1954 31 Claims. (Cl. 3155 .27)

The present invention relates to velocity modulation electron discharge tubes.

In known tubes of this type, the velocity of the electron United States Patent-O beam is modulated in a first circuit whereby the electrons become bunched. This bunching produces a high-frequency field in a second circuit to which the electrons give up their energy. This conversion of velocity modulation into density modulation occurs along the beam; the density of the electrons is uniform'in each transverse section of the beam; such a density modulation is termed longitudinal modulation.

The operation of tubes'based on this principle and constructed for millimeter wavelengths is not very satisfactory from the point of view of efiiciency and useful power. One of the main reasons for this'resides invthe necessity of giving the beam and in consequence the cathode negligible transverse dimensions relativeto the wavelength, thus making it impossible to use'intense beam currents. Further, the dimensions of ':the"va'rious elements of the tube become so small that it is diflicult to obtain suflicient precision in construction.

The present invention has for its Object to provide tubes which are adapted to operate within theaforementioned frequency range and are exempt from"these, disadvantages, in that they enable the use 'of cathodes whose transverse dimensions are of the same magnitude order as the wavelength. In the tubes embodying the invention, the electron beam is velocity modulated by an ultra-high frequency field in a modulatingspace. At the end ofa certain path, the conversion of velocity modulation into density modulation is effected. According to the invention, this modulation in density is transversal with respect to the electron beam. In other words, each transverse section of the beam comprises are'as"where the electron density is stronger than the mean density of the heartland areas where this density is weaker. On the other hand, .the mean electron densityof successive transverse sections is substantially the same.

The tubes according to the invention comprise another space, said collecting space, in which the transverse density modulation of the beam'induces another ultra high frequency field; the dimensions of the cathode, and of 2,972,701 Patented Feb. 21, 1961 Figs. 10,, and .10 areplaneand sectional views of a detail'of the tube "of Fig. 9; Figs. 11 to 13' are "longitudinal views of embod ments of oscillators according tojthe invention with ad usting means'for the oscillation frequency;

Fig. 14 is a viewin longitudinal section of an embody ment of a frequency multiplier;

Fig. 15 is a view in longitudinal section of an amplifier according to the invention in which the modulating ultrahigh frequency field is travelling; H y

Figs. 16 and 17 areviews in longitudinal section of subsequent improvements in the "circuits utilized;

Figs. 18 and 19 are similar views of two amplifiers having non-rectilinear circuits;

Fig. 20 is a cross sectional view of an oscillator of circular form;

Figs. 23 and 24 are similar views of two subsequent embodiments Of oscillators of circular form;

Figs. 21 and 22 are views of two subsequent embodiments of amplifiers, having non-rectilinear circuits;

Figs. 25 to 29 are side elevation views of five variants of magnets suitable fin the tubesaccording to the invention;

Figs. 30 and 31 are axial and transverse sectional views, respectively; of an oscillator of circular form operating witha'non-uniform magnetic field due to the circulation of current in an axial rod.

both modulating and collecting spaces, are of the magnitude order of the wavelength to be produced;

The invention will be better understood with'refere'nce to the accompanying figures in which:

Fig. 1 is a simplified view of. significant elements of the tube embodying the invention seen in longitudinal section, the operation of which is explained with reference to the diagrams shown in Figs. 2 2 3 and 4;

. Figs. 5 and 6 are respectively views of an amplifier seen in longitudinal and transverse sections, embodying the invention;

' Fig. -7 is a perspective view of a detail of the tube of Figs.5and6; r 1

Figs. 8 and 9' are respectively plane and sectional views of an oscillator embodying the invention; r

In Fig. l, a fiat emitting cathode'l is'seen in longitudi nal section. Disposedin' front of this cathode and'parallel thereto are two flat grids 3 and 4. Two other flat and parallel grids 7 and 6 are respectively disposed in the planes of the grids 4 and 3. A uniform magnetic induction field Bis oriented in a direction perpendicular to the plane Lof -thefigure. These four"electrodes are brought to a positive potential V relative to the cathode 1. An ultra high frequency 'field'is'set-up 'by any suitable means;'in'-the space 2 between the grids 3 and 4 in a direction perpendicular to these two electrodes, and it is desired to establish, in the space '5 between electrodes'fi and 7,;another ultra-high frequency field, said ultra-high frequencyfield being induced in the'space 5 by the transversely modulated beami In the ensuing description, for thesake of simplification, it will be supposed that the electrodes 3 and 4 are at such distance'from the cathode 1 that the effect the field B had on the electrons in the space between the electrodes 1 'and'4'may be'neglected and that, in other words, theelectrons emitted by the cathode l'traverse the spacezin a direction pe'r'pendicularto the grids 3 and 4..

- In'Figure 1- the cathode is'seenin longitudinal section and its length-l is substantiallykqual to the wavelength in the free space of theultra'-highfrequency fieIdset 'up'inthe'space 2. It will'al'so be'supposed,'firstly, that the ultra-high frequency fiel'd'is standing in-the sp'aceZ and that two nodes are established at the two ends A and E of the cathode, an intermediate node being situated mid-way between these two nodes.

unit operatestin the following manner? According to. the foregoing hypothesis, the electrons emitted bythe'jcathode 1. traverse-the space 2 ma direction perpendicular to theelectrodes 3 and 4. The mean velocity of all the electrons at the output end of the modulating space 2 is'governed by the potential 'V, but some of these electrons'are retarded and others accelerated by the modulating: field in accordance-with the well-known phenomenon of velocity modulation by an ultra-high frequency field.

The electron trajectories-or paths are thereafter incurved in the drift space'between the electrodes 3-4 and .7-,-6 as. a result; of i116? action of the field B and assume the form of arcs of circles. After having travelled along a semi-circle whose radius is proportional to their initial velocity at the outlet end of the space 2, the electrons attain the space between the electrodes 6 and 7. Now, it is well known that the time taken by the electrons in travelling along a semi-circle in a space in which a uniform magnetic field prevails, is constant and is independent of their initial velocity, in this space, the angular velocity along this semi-circle, depending only on the intensity of the field; the initial velocity has determined the radius of said semi-circle.

Thus the electrons emitted at the same instant t by the cathode 1 reach the space 5 at the same time. Assuming that a, b, c, d and e are the semi-circles travelled through by the electrons emitted respectively by the cathode in front of the nodes A, C, E and of the antinodes B and D, of the ultra-high frequency field on the cathode, it is obvious that the radius of the circles a, c and e is constant with respect to time, the action of the high-frequency field having no effect on the corresponding electrons.

If the configuration of the ultra-high frequency field along the cathode is as seen in Fig. 2,, at a time t (maximum positive amplitude at the antinode B, and maximum negative amplitude at the antinode D) the circle b would have maximum radius, the electron emitted at B having been subjected to the greatest acceleration of the part of the ultra-high frequency field. Similarly, the circle d would have minimum radius, the electrons emitted at D having been subjected to maximum deceleration by the ultra high frequency field. T being the period of variation of the ultra-high frequency field, at the time the configuration of the field is as plotted Fig. 2

It is obvious that in the course of one total period of variation of the field, the circles a, c and e maintain a constant radius, the circles b and d having a radius which varies in accordance with a sinusoidal time law from a maximum to a minimum.

If at the time t, the field has the configuration shown in Fig. 2 the semi-circle b has a maximum radius, the semi-circle d minimum radius, and the ends of the corresponding trajectories B, D are displaced nearer to the end C, of the semi-circle c.

It is clear, therefore, that in the vicinity of point C there is a region of maximum electron density at time t+0, 0 being the constant time taken by the electrons in travelling from the space 2 to the space 5. e

In the foregoing description, it was implied that the ultra-high frequency field was nil at the nodes, or, in other words, that the field was perfectly standing. It is clear that if this hypothesis is not actually fully realized, the phenomena would be qualitatively the same.

Figs. 3 and 4 show the network of electron trajectories at the two successive instants t and the density is uniform, the ultra-high frequency modulat ing field being overall nil, and having no action over the electrons.

4 Therefore it can be understood that the density has a maximum variation during a period of the modulating ultra-high frequency field in the vicinity of A, C and Thus there is established in the space 5 by means of induction, another ultra-high frequency field termed a collecting field which is standing and of which the respective antinodes are A, C and E'.

A first embodiment of an amplifying tube of the invention is shown in longitudinal sectional and cross sectional views, respectively, in Figs. 5 and 6. In these figures the same reference numerals designate the same elements shown in Fig. l.

The tube comprises in an evacuated metal envelope 14 a cathode 1 having a filament 9 fed by conductors 10. An electron lens 8 focuses the electronic emission in a direction perpendicular to the cathode. The space 2 and its two grids 3 and 4, hereinafter termed the modulating circuit, are disposed just about the cathode. The space 5, where the amplified energy is received, is disposed in such manner that the grids 5 and 6 are respectively in the planes of the grids 3 and 4. These two circuits are separated by the electrode 31. A collector 18 captures the electrons. A source of direct current voltage 33 has its negative terminal connected to earth and, furthermore, to the unit 2, 5, 14, 18 and 31.

The envelope 14 is disposed between two polar pieces 32 (Fig. 6) which create a magnetic field B in the envelope which is perpendicular to the plane of the Fig. 5. A water jacket 15 comprising an inlet 16 and an outlet 17 serves to cool the unit.

A section of a wave guide 11 coupled to an ultra-high frequency source not shown, terminates in space 2. Likewise, the circuit 5 is coupled to an output 12. Windows 13 render the envelope vacuum tight.

Fig. 7 shows, in perspective, the circuit 2. The latter has the shape of a prism made of metal comprising a reentrant portion. This reentrant portion is closed by the electrodes 3 and 4 in the form of grids. The circuit '5 not shown has an identical shape.

Theoperation of this unit is obvious from the foregoing description. The wavelength of the operating frequency is governed by the longitudinal dimension of the circuit 2. The length of the electrode 31 is selected in accordance with the field B and the applied potentials, in such a manner that all the electrons crossing the space 2 impinge the collector 18, after passing through space 5. These factors determine the radii of the circles a, c and e by well known methods. a

The circuit 2 is closed by a short-circuit 31. A standing electromagnetic field is established therein. If the length of the circuit is appropriate, this field will oscillate and a field node will be established at the two ends.

Likewise, in the circuit 5, a node will be established at the end 31. But it is clear from the foregoing description that if the circuit 2 vibrates with the nodes facing the two ends of the cathodes, the circuit 5 vibrates with the antinodes situated at the limits of the impacts of the electrons.

Figs. 8 and 9 show in longitudinal sectional and horizontal cross-sectional views, respectively, a self-oscillating tube embodying the invention. The circuits 2 and 5 are two cavities shown respectively in cross-section and plan in Fig. 10. Like reference numerals designate like elements in Figs. 5 and 7. A coupling between the cavities 2 and 5 is established by means of a coaxial line 19 which terminates at each end in a coupling loop 20. This coupling creates a feedback between the spaces 2 and 5. The tube comprises a single ultra-high frequency output 12 in the form of a guide. The frequency of the oscillations may be adjusted by means of slightly deforming the circuits 2 and 5 by conventional means.

Figs. 11 to 13 diagrammatically illustrate some oscillators embodying the invention.

In Fig. 11 the circuits 2 and 5, which are in the form of aera or two portions of a rectangular wave-guide having the same cro'ss section are connected-by e wave guide'22 having a smaller cross-section. This guide 22 couples the spaces 2ar1d5 to'each other and creates the feedback necessary for sustaining oscillations. In practicejtheguide 22 is obtained by means; of ablock23 disposed between the portions of guides 2'and'-5.-" Th'e length and the height of this block govern the phase and amplitude of the-feedback. The energy is obtained at the output -12- of the guide 25.' I 'fIn'Fig. l2 there-is also provided, in derivation with the guides 2 and 5, a guide portion 34 which emerges from the tube. A window 13 disposed in wave portion 34, renders the tube vacuum tight. A piston disposed in the part of the guide 34 outside the tubef'allows the adjustment of the feedback.

The tube shown in Fig; 13 is similar to that shown in Fig. 11 but the position of the block 23 is adjustable by means of a mechanical system comprising a rod 24' which is slidable inside a bellows 25. In tightening the nuts' 35, pressure isbrought to bear on the plate 3 6 andthe'trod 24, rigid with the block 23, is displaced whiehpermits adjustment of the feedback. I

The tubes embodying the invention are also applicable to frequency multiplication. Fig." 14 shows merely by way of example a frequency doubler. It differs from the amplifier shown in Fig. only in respect of the circuit 5 which, instead of permitting a free passage with respect to the electrons over its entire surface, comprises apertures 26 permittingsuch passage in certain regions while preventing it in other regions. The length of this space is equal to 1.25%, A being the wavelength: of the operating frequency. The apertures 26 are disposed at distances from the left end of the circuit 5 which are re- The left end of the circuit 5 is short-circuited and an .Referring to Fig. 1, it can befseen that at the instant t,

the field is distributed along the cathode in the manner shown in Fig. 2a, At this instant, the density bunching is obtained in the same manner as inthe case of the standing field. At instant t-I-At, this field pattern is displaced towards the right, for example, of a length AS which is equal to vAt, v being the velocity of the travelling field- In the collector circuit the maxima of the field are displaced in the same manner and at the same velocity v as the maxima of the modulating field. a travelling field is established on condition that the collector circuit is closed on its wave impedance and that, furthermore, the field is capable of being propagated at the velocity v. Hence it is necessary that the ultra-high frequency parameters of the two circuits be identical.

Fig. 15 shows an amplifier in which ther'nodulating field is travelling. This tube on the whole comprises substantially the same elements as the tube shown in Fig. 5 which carries the same reference characters. It comprises a very long guide 27 to which a travelling wave is fed at 11, along this guide there being disposed several identical cathodes 1 which are separated by a distance which is a whole number multiple of he, Ac being the wavelength in the guide of the travelling field. Further, the field B is so selected that the electrons emitted from one cathode strike the homologous point of the following cathode, in the absence of the ultra-high frequency field.

As it travels, the wave velocity modulates the beam the same beam which is density modulated transversely at the end of its semi-circular trajectory. The amplified "at 12 a wave which has undergone several successive amplifications. In order to reduce the risk -of selfoscillations, a localized attenuation 28 is disposed in the guide 27 between two cathodes 1. The respective dimensions of the circuits are'so selected as to avoid harmful electron impacts. 1

In Fig. 16, plates -37 have been disposed in such manner as to receive the electrons that have traversed the induced ultra-high'frequency field. The source of voltage 38 brings them to the same direct current potential less than that of the circuit 5. They are preferably disposed in front of-the voltage nodes in the circuit' S. The electrons that traversethe circuit 5 in the'vicinity of these nodes have not given up much energy to the ultra-high frequency field and have not in consequence lost kinetic energy. Thus, it is advantageous to retard them so as-to'lose as little energy a's possible at the moment of their capture. 1 l

It is possible to design tubes embodying the invention 'with cathodes andcircuits having,-in the direction-perpe'ndicular to the plane of the Figs. 1, 5 and 8, a dimension of the order ofthe operational wavelength. Fig. 17 shows a sectional view, taken on aplaneparallel to the lines of force of the magnetic field, i.e. on a plane perpendicular to the plane of Fig. 5, of a space or circuit 2 employed in these tubes. -There may be seen in this figure several systems of electrodes -3-" 4, excitation also being possible in a standing high-frequency'wave mode.

"The grids 34 are disposed infront of the antinodes particular of their initial velocity in the' space without electric field and electromagnetic field.

' It' is, however, difficult to construct tubes, having cathode, and accelerating electrodes, i.e., grids 3 and'4 in very close proximity. The potential V can beof the order of 1000 v. relating to the cathode and breakdowns can occur. 1

In the ensuing description, the case in which. the cathode 1 and the electrodes 3 and 4 are sufficiently spaced apart for avoiding such breakdowns, and located in such manner that it is no longer possible to neglect the action of the magnetic field Ben the electrons travelling between the electrodes 1 'and'4, is examined.

Electrons emitted by the cathode 1 are'in this case subjected in the space 2 to the joint action of the highvfrequency field and the field B and enter the drift space,

between electrodes 3-4 and 6-7, the angles between the respective trajectories and electrodes 3 depending on the phase of the modulating field at the instant of emission and of the emission point of the cathode. Actually, the direction of electron trajectories is no more normal to electrodes 3 and 4 and parallel to the lin'esof force of the ultra-high frequency field. The trajectories in this space are no longer semi-circles, the arcs travelled along dependingon the phase of the high-frequency field, and the transit time is no longer constant. It may be shown that the transit time varies, between an upper and a lower limit, about a mean value i.e. is modulated.

Theory and experience show that, for the tube according to the invention to operate correctly, the transittime between the electrodes 2 and 5 has to 'be the same for all the electrons. I g

It may also be demonstrated that for certain difference values between the respective transit times of ,theelectrons, the resulting bunching is such that the tube operates substantially as described above. These values may be determined by experiment. I

To this end electrodes 6 and 7 of the collecting circuit may be disposed as shown in Fig. 18, i.e., in

planes parallel to the planes of the electrodes of the modulating circuit 2, but vertically raised away from the plane of the cathode 1.

As shown in Fig. 19, it is also possible to give the guide 1112 an incurved form with the convexity directed towards the cathode 1. Compared with the tube shown in Fig. 5, such tubes have the advantage of requiring weaker magnetic fields, for the same mean transit time of the electrons.

In the tubes shown in Figs. 18 and 19, the trajectories 41 are clearly'shorter than a semi-circumference and the electrons in travelling along these trajectories within a given mean transit time require a Weaker magnetic field than if the-respective arcs were semi-circles. For the same transit time, angular velocity is lower when the angular trajectory is shorter and it is well known that the angular velocity is proportional to the magnetic deflecting field.

Fig. 20 shows an oscillator derived from the amplifier shown in Fig. 19. circle, each cathode 1 being situated at the apex of a square disposed outside this circle. The structure of the system is symmetrical about an axis perpendicular to the plane of the figure. A guide 12 serves as an ultrahigh frequency output. However, in the present case, the guide 27 forming a complete loop, a standing ultrahigh frequency field will be induced more easily than a travelling field. A short circuit 29 fixes the position of a voltage node in the guide and hence the position of the nodes and anti-nodes of the standing field produced in this guide and, in consequence, the positions of the cathodes and of the grids. This oscillator permits the magnet necessary for its operation to be smaller.

Instead of making the electron trajectories smaller than half a circle, it is also possible, as shown in Figs. 21, 22 and 23, to keep these trajectories substantially equal for all the electrons, in spite of the fact that, as mentioned above, the respective angles of incidence of these trajectories on the electrodes 2 differ from each other.

The tubes shown in Figs. 21 and 22 are respectively analogous to those in Figs. 18 and 19, but in Fig. 21, the circuit 5 is lowered with respect to the circuit 2 instead of being raised. In Fig. 22, the guide 11--12 is incurved, its concave side facing the cathode.

In Fig. 23, the cathodes are placed at the corners of a square within the circle 27.

Owing to the vertically-staggered arrangement of the circuits 2 and '5, the electron trajectories-if the electrons were to enter the drift space with a direction perpendicular to the electrode 3would be longer than semi-circles.

This would result, neglecting the distance between the electrodes 1 and 4, in a modulation of the transit time.

It may be shown that this modulation of the transit time may be compensated by the effect of modulation of the transit time due to the distance between the electrodes, for a convenient value of the accelerating field V and the deviating field B. In other words, if the values V and B are suitably chosen, the electron trajectories are as shown in Figs. 21 through 23 again semi-circles, the latter being no longer normal to the electrodes 3 and 4. The modulation of the transit time is thus eliminated; the modulation of the beam is therefore effected in conditions similar to those prevailing in the tube shown in Fig. 5.

Fig. 24 shows an oscillator which is similar to that shown in Fig. 20, but which comprises an additional cylindrical electrode 42 insulated from the other electrodes of the tube. v

This electrode is brought to an adjustable potential which is somewhat higher than that of the electrode 27, by means of the potentiometer 43 and a source 44, whose terminals are respectively connected to the ends of the potentiometer 43. Thus there is obtained in the drift The guide 27 is in the form of a 8 space 4227 an electrostatic radial field whose lines of force are oriented, according to the setting of this potentiometer, in the direction 27--42 or 4227. If they are in the direction 4227 (the potential of the electrode 42 being greater than that of the guide 27) the electron trajectories 41 are no longer arcs of circles so that the electrons approach the electrode 42. The transit time is therefore increased.

Theory and practice show that, by suitably adjusting the potentiometer 43, the transit times of the electrons may be made independent of their initial velocity in the space and operation is as though the trajectories were semi-circles.

Similarly, if the direction of the lines of force is 27-42, the electron trajectories recede from the electrode 42 and are shortened. The transit times are reduced andby means of a suitable adjustmentit is possible to obtain the optimum values of the transit time indicated above.

Similar results may be obtained by imparting to the lines of force of the magnetic field in the drift space a suitable pattern instead of using a uniform field as in the foregoing examples.

To this end, polar elements 32 may be used which are convex (Fig. 25) or concave (Fig. 26) or annular (Fig. 27), the result obtained with annular elements being the same as that obtained with the elements shown in Fig. 24. All these elements may be used with a cylindrical tube 14 such as for example those shown in Figs. 20, 23 or 24. The axis of the cylinder is indicated at AA. In the case of tubes having a rectilinear structure, the polar elements may have an incurved shape such as those in Fig. 28 or 29, which shows the system in the same way as Fig. 6. The cathode is assumed located at the base of the figure. The distance between the polar elements increases and the magnetic field decreases when approaching the cathode in Fig. 28 and receding from the cathode in Fig. 29.

If it is desired to reduce the mean transit time of the electrons, for example so as to bring it to its optimum value, it is necessary to subject the electrons in the drift space to a magnetic field which is the stronger as the electrons are further from the cathode. The effect of such a magnetic field is to accentuate the mean curvature of and hence shorten the trajectories.

Conversely, if it is so desired to lengthen the electron trajectories so as to compensate various factors affecting the transit time and hence render them independent of the initial velocity of the electrons in the drift space, there is created in the drift space a field which is such that the electrons are subjected to a field whose intensity decreases with recession of the electrons from the cathode. The effect of this field is to decrease the mean curvature of and hence lengthen the trajectories.

In the first case, the magnets shown in Fig. 25 may be used with the tubes shown in Fig. 20 or 24, or the magnets shown in Fig. 26 or 27 used with the tube shown in Fig. 23. The magnets shown in Fig. 28 would be used with the tube shown in Fig. 5.

In the second case, the polar elements shown in Fig. 25 are used with the tube shown in Fig. 23 and the elements shown in Figs. 26 and 27 with the tubes shown in Fig. 20 or 24 and those shown in Fig. 29 with the tubes shown in Fig. 19.

Figs. 30 and 31 are axial sectional and cross-sectiona views respectively of another embodiment of an oscillator tube in which the electrostatic and magnetic fields in the drift space are non-uniform, the two abovementioned effects being combined.

The metal cylindrical envelope 14 contains, axially disposed therein, and insulated therefrom, a metal rod 42. The latter is connected between the terminals of a source of low voltage alternating energy 44 and, furthermore, to a tap of a potentiometer 43 by means of which it is possible to bring the rod to a positive or' manner defined hereinbefore.

the latter an alternating magnetic fieldwhose lines of force are coaxial with the tube, the intensity of the field decreasing'with recession from the rod. The positive,

vor negative, potential appliedto the rod results in the creation in the drift space of a radial electric field similar to that shown in Fig. 24.

disposed in the median plane of the latter. Guides 27 .are disposed on a cylinder coaxial with the envelope 14 and extend in adirection parallel to the generatrices of this cylinder. They are connected to the envelope 14 so as to' be brought to the same potential as the latter. Each guide is disposed'o-pposite the corresponding cathode. These guides are disposed side by side and coupled together by apertures 45. One of the guides is provided with an output 12 the passage through the envelope being closed by an insulating window 13. Each guide comprises a modulating circuit 2 and two collector circuits 5, disposedon either sideof the modulating circuit; these circuits are, for example, of the type shown in Fig. 7. The electrons from the cathodes 1 pass through the circuits 2 and, under the action of the non-uniform alternating magnetic field, describe trajectories attaining the collector circuit 5 or the circuit 5', according to the alternations. The shape of these trajectories is also affected by the adjustable radial electric field; the cathodes 1 are unblocked by the pulses of the negative potential relative to the potentials of the guides 27. These pulses are applied by a source 46 which is synchronized with the source 44 by means known per se and generally indicated by the dot-dash line 47. The

. source 46 produces a pulse for each positive or negative peak of the voltage furnished by the source 44. The electrons therefore follow alternately the trajectories '41 hand to microwave electron tubes utilizing either a single pair of microwave circuits corresponding to the circuits '2 and 5 of Figure 1, or, on the other hand, although at least one pair of such circuits is essential, a plurality of intercoupled pairs of circuits may be utilized in the manner illustrated in connection with Figures 15, 20, 23, 24, 30 and 31. t

In Figures 15, 20, 23 and 24, the respective pairs of circuits are arranged end-to-end and intercoupled in the In Figures 30 and 31, not only are the pairs of circuits 2, 5 and 2, 5'- connected end-to-end, but these pairs are also arranged circumferentially side-by-side, as is obvious fro-m the axial view ..-of Figure3l, the first circuits 2 forming an annular-ring and the second and third circuits 5 and 5, respectively, also forming annular rings on opposite sides of the circuits 2, each of these annular arrangements being coaxial with respect to the axis of the conducting rod 42 ,and axially spaced therealong;

. circiuts ofeach pair.

This'applic'ation is adivisiori of my application Serial f No.'506,3 1.7; filed 'May 5,1955, now'U.S. Patent No. 2938.139. a

What I claim is: l. A microwave electron tube comprising within an evacuated envelope a plurality of operatively intercou 1'0 pled pairs of microwave circuits; each said pair of circuits comprising a firstcircuit and a second circuit extending in a predetermined direction, electron emissive means positioned along each said first circuit for emitting a sheet-like electron beam in coupled relationship with said first circuit, means for feeding microwave energy to each said first circuit to'provide amplitude differences of an ultra high frequency field at different points along each 'said first circuit for simultaneously velocity modulating electrons in the respective beams at said dilferent points in accordance with the amplitude of the ultra high frequency field at the respective points,

means for establishing within said envelope a magnetic from therespective first circuit in coupled relationship with said beam, each said second circuit being of suflicient length and so disposed as to be acted upon by different densities of the electron beam transversely of the latter and along said second circuit, said different densities being representative of the high frequency field in a respective first circuit, thereby to induce a microwave field within each said second circuit and coupling means to said induced fields for utilizing the energy thereof.

- 2. A microwave electron tube according to claim 1, wherein said coupling means includes means. for coupling together the microwave fields of said first and second circuits and means for coupling an external load to one of said circuits. 1

3. A microwave electron tube according to claim 1, wherein said coupling means includes means for coupling the induced microwave field of one of said second circuits to one of said first circuits.

4. A microwave electron tube according to claim 1,

wherein said pairs of microwave circuits are arranged side by side.

5. A microwave electron tube according to claim 1, wherein said pairs of microwave circuits are arranged end to end.

6. A microwave electron tube according to claim 1, wherein said electron emissive means are spaced angularly about an axis of the tube at stations corresponding to apices of a regular polygon.

7. A microwave electron tube according to claim 6, wherein the lines of force of said magnetic field general- 1y circle said axis in planes substantially perpendicular thereto.

8. A microwave electron tube according to claim 6, wherein said magnetic field extends generally parallel to said axis.

9. A microwave electron tube according to claim 1,

wherein said pairs of microwave circuits together define a generally circular arrangement.

10. A microwave electron tube according to claim 9, including means for mutually coupling at least some of said circuits to each other circumferentially of said circular arrangement. I

11. A microwave electron tube according to claim 9, wherein said firstcircuits are arranged in one circle and said second circuits are arranged in another circlegsaid circles being coaxial and axially spaced along the common axis.

cuits extend is generally parallel to said axis. 

